Following the confirmation that the second season of "One Punch Man" is under development, there have been no official details about the anime series' updated storyline. For now, the fans expect more action-packed adventures from the show's main character, Saitama. Unfortunately, they might also get ready to see the fall of their favorite hero in the hands of a new enemy.

Saitama is known to be the most powerful hero in "One Punch Man," and no fighter was ever able to withstand his raw power in the show's first season. However, rumors have surfaced online that Saitama's streak of undefeated bouts will come to an end in season 2. There are speculations that Saitama will be defeated by a character named Sonic. The new fighter has not yet been introduced in the anime series, but followers of the manga version might already be familiar with Sonic.

Reports suggest that Sonic will be seen throwing knives at Saitama in one episode of "One Punch Man" season 2. The full extent of Sonic's power is not yet known, although the character's backstory in the manga reveals that he was trained by a Shinobi, therefore increasing his chances to defeat a powerful hero like Saitama.

Sonic is believed to get his immense power from consuming the Monster Cell. By doing so, he will have the same strength and abilities of a monster, therefore giving him more advantage in a fight with Saitama. However, the manga still has not yet shown Sonic transforming into a monster himself. 

Aside from Sonic, the other potential rival of Saitama in "One Punch Man" season 2 is Garou. According to Inquisitr, Garou could be the next major villain of the anime series, as he possesses the qualities opposite to Saitama. As Saitama enjoys being a hero to have fun, Garou is described as an evil character that hunts down heroes for his own selfish reasons. Nevertheless, Garou still maintains his morality especially in one chapter in the manga where he saved a child from the Monster Association by risking his own life.

Fans still have to wait a little longer to watch the all-new episodes of "One Punch Man." Season 2 is expected to be released in 2018.